It is well known that in a two-for-one twisting spindle the yarns to be twisted together are unwound upwards from at least two bobbins located on a fixed mandrel. This known unwinding operation has the drawback of causing the yarns to interfere with each other and become tangled before entering the central hole in the spindle, thus forming loops, rings, spiral corkscrew-shaped portions and shapes of this kind. It is also well known that the unwinding yarns in a two-for-one twister, especially of high-speed operation, are exposed to tension variation which is sometimes excessive. If several yarns are concerned, whether yarns spun from flock or synthetic filament yarns, this excessive tensioning is undesirable because the yarns undergo severe stressing and friction contact whenever they tangle during their continuous unwinding from the feed bobbins, and they consequently become excessively stretched, damaged or in the limit broken. This generates interruptions in the production process and therefore impairs the economics and productivity of plants of this kind.
Two-for-one twisting spindles of this construction have the further drawback that the yarn is caused to rest and slide on the outer peripheral surface of the feed bobbins, thus damaging the yarn by abrasion and reducing its strength. There is therefore the danger that this intersecting of the yarns, which as they unwind rotate in orbits about the spools, and the aforesaid sliding along the outer peripheral surfaces of the bobbins themselves, lead to the formation of flying dust and fibrils, which after a certain time become twisted together with the yarn and can result in twisting defects. Again, this repeated yarn intersection and obstruction and the said frequent sliding contact along the outer surfaces of the feed bobbins can result in a greater energy requirement per spindle and therefore an increased cost of the twisted yarn product. Many attempts have been made to ensure that the yarns unwinding from the bobbins mounted on the bobbin carrier coaxial with the hollow spindle do not undergo mutual interference and obstruction during their orbital unwinding rotation before penetrating into the open end of the spindle. Typical examples of these attempts of the known art are the unwinder arms positioned at the top of the spindle shank or in the middle between the superposed feed bobbins, or alternatively at the bottom below the unwinding bobbins.
The arms are entrained by the yarns and rotate about the spindle shank by being centered thereon, and for a considerable time have been used as an unwinding and guiding aid for the yarns to be twisted. In addition, discs or plates of various shapes are known which, centered and positioned horizontally about the spindle at its top or in the middle between the superposed bobbins, guide the yarns to be twisted by separating them from each other along the path between the unwinding zone and the top zone in which they enter the spindle.
The use of such yarn guides does not represent a satisfactory solution to the problem in the production of twisted yarns in two-for-one twisting spindles.
In this respect, these known-art applications frequently result in non-uniform twisting because of the variation in yarn tensioning conditions deriving from the different and intricate guiding of the individual unwinding yarns. This effect is undesirable because it ruins the appearance of the twisted yarn and also results in a reduction in its resistance to tear because the individual yarns when subjected to a pulling force undergo nonuniform loading. In the case of very thin yarns undergoing particularly rapid unwinding, this can result in breakage. In addition, the aforesaid known devices are rather complicated in their construction and application and are also rather difficult to use. They are in fact of more costly construction and more complicated to handle than the unwinder element of the present invention.
An object of the present invention is to obviate the aforesaid drawbacks by providing an unwinder arm for a two-for-one twisting spindle producing twisted yarn, which has the following advantges:
it eliminates the formation of loops, rings and spiral corkscrew-shaped portions while maintaining the tension in the yarn unwinding from the feed bobbin substantially constant; PA1 it reduces breakages to a level substantially lower than any other known unwinder element, by making the yarn unwind in a more suitable manner; PA1 it enables any yarn structure, including cotton, to be twisted on a two-for-one twisting spindle operating by direct twisting, practially without regard to its composition or structure; PA1 it allows yarns unwinding from bobbins of considerable axial length and taking any unwinding path to be guided separately for twisting purposes; the limit depends only on the dimensional ability of the twister to hold the bobbins;
it enables the twister to use conical feed bobbins of any angle up to 5.degree. 57.degree. and also allows the twister to use two superposed bobbins with yarns of different fibre and of different count, because the braking of the unwinder element of the present invention, done by systems of the known art, is independent of the braking of any other unwinder elements which may be present. A further advantage of the unwinder element of the present invention, acting as an unwinding aid for the yarn which rotates it, is that it guides the yarn and enables it to run at the correct distance from other feed yarns, so that there is no possibility of the yarn guided by it intersection the other yarns, with the result that it does not rub against them and is therefore not subject to wear. This latter advantage enables a twisted yarn to be obtained which is of improved quality at lower operating cost. This improved quality derives from the lack of sliding contact between the individual yarns with consequently no generation of dust or flying fibrils, as the individual yarns take different paths during the entire unwinding stage. In this respect, the guide eye at the end of the unwinder arm of the present invention guides the yarn unwinding from the lower bobbin in an upper rotary orbit surrounding the rotary orbits of the other unwinding yarn or yarns.
In practice it is a substantial advantage if the unwinder arm of the present invention together with its support can be instantly mounted on the box containing the two or more superposed bobbins and can be likewise instantly removed, is said unwinder arms must be mountable and removable without effort. This can be done for example by providing the unwinder arm support at its bottom with a strip in the form of a circular band which can be elastically mounted on the upper edge of the bobbin box. Thus tools are not required either for mounting the unwinder element of the present invention on a two-for-one twisting spindle, or for removing it therefrom. Thus no constructional modification is necessary in order to be able to mount said unwinder element on an existing two-for-one twisting spindle.